DENSITY OF THE HYDROSPHERE 179 



within the belt of cementation is a slow one, and much of the CO2 

 therefore remains unused and issues again on the surface. The 

 mineral springs of the Auvergne district of France alone furnish an 

 amount of CO,, estimated by Lecoq at 7.000,000,000 cubic meters 

 per year, and these represent only a small fraction of the carbonated 

 waters of the world. Carbonation, or the production of carbonates, 

 is, on the whole, one of the most important chemical reactions within 

 the zone permanently occupied by the ground water. 



DENSITY AND SPECIFIC GRAVITY OF 

 THE HYDROSPHERE. 



Pure water (distilled) has its greatest density at a temperature 

 of 4° C, and this is taken as the unit of measurement, or i. (Its 

 salinity is o, and this may be expressed by S', while that of any 

 other water is expressed by S.) The addition of dissolved substances 

 increases the density of the water, which in the case of normal sea 

 water of 35 permille salinity (35 gr. of salts in 1000 gr. of sea water) 

 at 0° C. becomes i. 02812. This is expressed by the following 



S 0° I .02812 

 formula: ^7— 3 = = i. 0281 2, where S o represents the 



04 ^ 



density of the water in question at 0° C. and S' 4° that of pure water 



at 4° C. For convenience sake we may transform the above formula 



/S 0° \ , , , , , 



mto: 1000 (-^7 — J — I ),and express the result by the symbol o-q- 



Thus for normal sea water of 35 permille salinity (^o = 28.12, while, 



if the salt were NaCl only, o-q would be 26.67. If wholly MgS04, o-q 



/S t° \ 

 would equal 36.94. The general formula is a-^ = 1000 (^r~3 — i ) 



where t = the temperature at which the density of the water in 

 question is taken. For sea water where o-q = 28 *, 0-4 = 27.68, 0-15 = 

 25.87, 0-15.5 = 25.76 (approx.), or25 = 23.24. 15° is the temperature 

 for which the hydrometers used in foreign laboratories are usually 

 graduated, while those of English and American use are graduated 

 for 60° F. (15.56° C). Many of the newer instruments are arranged 

 for the more usual temperature of laboratories, which is 25° C. or 

 77° F. For the same temperatures, distilled water has the following 

 densities: 0° C. (32° F.) 0.99987, 4° C. (39.20° F.) i. 00000, 15° C. 

 (59.00° F.) 0.99913, 25° C. (77° F.) 0.99707. (See the table given 

 in Kriimmel— 20, 252-255.) When the salinity is known o-q may be 



*28 instead of 28.12 is used, since the tables of Knudsen given by Kriimme 

 are not calculated for decimal values of <r,,. 



